Abstract of Thesis presented at COPPE/UFRJ as a partial fulfillment of the requirements for the degree of Master of Science (M.Sc.)

Control of a Machine of Fatigue Testing of Materials Driven by a Linear Motor

Alcidney Valério Chaves

October/2014

Advisors:

Ramon Romankevicius Costa Alessandro Jacoud Peixoto

Department:

Eletrical Engineering

      Given the changing demands of the industry for materials that support work in environments increasingly aggressive, it becomes essential to develop tools that assist in the characterization of these materials, such as fatigue testing machines. This dissertation addresses the modeling, simulation and control of a fatigue test machine driven by linear motor. After a literature review on fatigue tests and linear motors, a simulator is developed with parameters obtained from the control literature and manuals of linear motors manufacturers. The stiffness of the specimen is time varying due to the crack propagation. Based on experimental data, it is assumed that the specimen behaves as an equivalent spring which varies slowly in time. It is proposed the usage of a Linear Quadratic Gaussian controller (LQG) with integral action, as a promising alternative for the force tracking control of a fatigue machine driven by linear motor. In order to attenuate the effects of the time varying stiffness in the tracking performance, the controller gains are modified along time as a function of the tracking error and of a stiffness estimate obtained by using force/position measurements. Via numerical simulations, it appears that the slow variation of the stiffness ensures that the proposed scheme keeps the tracking force within the limits required by the standards of the fatigue tests. Therefore, it is possible to infer the feasibility of using these motors as actuators of fatigue test machines, in view of the current market trend which uses linear motors.